watchdog: hpwdt: eliminate section mismatch warning

hpwdt_init_nmi_decoding() is called in hpwdt_init_one error handling,
thus remove the  __devexit annotation of hpwdt_exit_nmi_decoding().

This patch fixes below warning:

WARNING: drivers/watchdog/hpwdt.o(.devinit.text+0x36f): Section mismatch in reference from the function hpwdt_init_one() to the function .devexit.text:hpwdt_exit_nmi_decoding()
The function __devinit hpwdt_init_one() references
a function __devexit hpwdt_exit_nmi_decoding().
This is often seen when error handling in the init function
uses functionality in the exit path.
The fix is often to remove the __devexit annotation of
hpwdt_exit_nmi_decoding() so it may be used outside an exit section.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Thomas Mingarelli <Thomas.Mingarelli@hp.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>